ABSTRACT CHARACTERIZATION AND IDENTIFICATION OF BACTERIOCINS FROM TWO LACTOCOCCUS LACTIS SUBSP. LACTIS STRAINS Ak&ccedil / elik, Oya M.S., Department of Biotechnology In this study, bacteriocins from two L. lactis subsp. lactis isolates of Turkey origin designated OC1 and OC2, respectively, were characterized and identified. The activity spectra of the bacteriocins were determined by using different indicator bacteria including Listeria, Bacillus and Staphylococcus spp. Bacteriocins were tested for their sensitivity to different enzymes, heat treatments and pH values. Loss of bacteriocin activities after &amp / #61537 / -amylase treatment suggested that they form aggregates with carbohydrates. Molecular masses of partially purified bacteriocins were determined by SDS-polyacrylamide gel electrophoresis. PCR amplification was carried out with different primers for the detection of structural genes of lactococcal bacteriocins. As a result of these studies, the two bacteriocins were characterized as nisin and lacticin 481, respectively. Association of the bacteriocin production with plasmid DNA was examined by using acriflavine as a plasmid curing agent. Plasmid profiles of the wild type and its non-bacteriocin producing mutants were determined by using the alkali lysis method followed by agarose gel electrophoresis. The genetic nature of industrially important characteristics of Lactococcus lactis strains were investigated through gene transfer studies via conjugation. According to the results of plasmid curing and conjugal transfer trials, it was concluded that in Lactococcus lactis subsp. lactis OC1 strain a 39,7 kb plasmid is responsible for nisin production, lactose fermentation and proteolytic activity. In Lactococcus lactis subsp. lactis OC2 strain, on the other hand, a 16 kb plasmid appeared to be responsible for lacticin 481 production and lactose fermentation.

Antimicrobial resistance (AMR) is concerning because it limits antimicrobial drug treatment options. AMR occurs by the overuse and misuse of antimicrobial drugs. In environmental settings, AMR can disseminate from places of high use, which leads to increased exposure to humans and animals. A previous study from our laboratory group showed extended-spectrum cephalosporinase-producing Escherichia coli/Klebsiella pneumoniae were isolated from fecal samples obtained in rural Cambodian community settings. Based on these isolates, this study has two aims. The first aim was characterization of selected Cambodian isolates with random amplification polymorphic DNA (RAPD) and antibiotic susceptibility test. From RAPD, the selected six isolates are diverse, except for C61 and C66 bacteria isolates with potential clonality. Additionally, the selected isolates are multidrug resistant (MDR) with reduced susceptibility to beta-lactams and fluoroquinolones. The second aim was to assess two developed methodologies, multiplex automated genome engineering (MAGE) and One-Step Curing Plasmid, by validation in bacteria laboratory strain and development for six Cambodian isolates. To modify AMR genetic elements, MAGE uses pMA7-SacB for homologous recombination with oligos for chromosomal gene disruption. Meanwhile, One-Step Curing Plasmid uses pFREE with the CRISPR/Cas9 system for plasmid and self-curing. Validation showed that MAGE can modify 8% of E. coli MG1655 with lacZ control screening oligos and almost 90% are cured from pFREE. Selected Cambodian isolates have antibiotic-resistance plasmids of IncR or IncFII replicon. For usage in Cambodian isolates, pFREE was modified to be pCAM-FREE by cloning IncR and IncFII plasmid as gRNA1 and gRNA5, respectively. Sequencing results showed pCAM-FREE have gRNA5. In conclusion, our study managed to characterize selected Cambodian isolates as MDR and diverse. In a laboratory strain, MAGE and One-Step Curing Plasmid are functional methods. Furthermore, pCAM-FREE was constructed to target IncFII and in the future, MAGE and pCAM-FREE could be tested in Cambodian isolates.